The basic DC power supply or battery charger plugs into a AC source via a wall receptacle and employs the use of a step-down transformer 104, signal rectification circuitry 106, and voltage regulation circuitry 108 as shown in FIG. 1. The transformer consists of two conductive independent coils that are mutually coupled by magnetic flux when current flows in one of them. The AC current flowing in the primary coil produces a changing magnetic field within the transformer core and there by induces an electric current in the secondary coil as described by Faraday's Law.
From transformer theory “no-load loss” is when energy loss occurs even when the secondary coil is left open or not attached to a load. According to academic literature the cause of no-load loss is attributed to eddy currents and magnetic hysteresis within the transformer core. In addition to no-load loss from the transformer, DC power supplies also incur dynamic and static power loss within the rectification and regulation circuitry. All of these combined losses within the DC power supply attribute to a significant portion of “vampire energy loss” which exists in many electronic product domains.
Techniques have been in place to reduce no-load loss within power conversion circuits; however the most effective way to stop no-load loss from the device charger is to take the DC power supply or battery charger completely off of the power grid.